Variable Stroke Length Electrically Operated Diaphragm Pump

ABSTRACT

A variable stroke length EOD pump system is provided that includes a diaphragm pump and an electromagnetic linear actuator that operates the diaphragm pump. The linear actuator includes two stator halves, and an armature. The armature is supported for linear motion along an axis of and between field poles of the stator halves. Each stator half may also include a drive coil partially surrounded by a magnetically permeable core.

RELATED APPLICATIONS

The present application is related to and claims priority to U.S. Provisional Patent Application, Ser. No. 61/781,335, filed on Mar. 14, 2013, entitled “Variable Stroke Length Electrically Operated Diaphragm Pump.” The subject matter disclosed in that provisional application is hereby expressly incorporated into the present application in its entirety.

TECHNICAL FIELD

The present disclosure is related to diaphragm pumps and, more particularly, to an electrically operated diaphragm pump having a reciprocating electromagnetic linear actuator.

BACKGROUND AND SUMMARY

Commercially available air operated diaphragm (AOD) pumps possess many desirable features. AOD pumps, nevertheless, also possess an inherent limitation—they require compressed air as a power source. Compressed air may not always be available in places where an AOD pump could be useful. Obtaining this power source requires an additional expense which may limit the pump's potential market.

Compressed air power also lacks efficiency. An air compressor compresses air (mechanical energy) to create stored energy. But the compressor is driven by electrical motors to convert electrical energy into the mechanical energy. Alternatively, an air compressor may be driven by a heat engine that converts chemicals into the mechanical energy. In either case, the resulting compressed air is distributed through pipes and hoses. Only after these energy expenditures does the AOD pump convert its stored energy back to mechanical energy (compressed air) which moves fluid through the pump.

Electrically operated diaphragm (EOD) pumps are a commercially available alternative to AOD pumps that mitigate some of the AOD pump's limitations, but introduce some of their own. EOD pumps employ speed reducing gear trains driven by conventional electric gear motors. These gear motors can operate at relatively high speeds allowing efficient energy conversion within the electromagnetics of the motors. The output of the gear trains then deliver mechanical energy through linkages to the pumping mechanisms at the relatively low speeds required by diaphragm pumps. The gearmotor EODs, thus, eliminate the need for compressed air and, thus, eliminate one of the energy conversion steps that waste energy. They also eliminate the additional cost of a compressor. On the other hand, using gear motors in EODs adds considerable size, weight, and expense to the pump when compared to an AOD. Commercially available gearmotor EOD's also typically have bypass springs that simply collapse when high outlet pressure places too much force against the diaphragms. This technique protects overloading the gearmotor, but does nothing to allow the pump to operate into higher outlet restrictions.

An illustrative embodiment of the present disclosure provides a variable stroke length EOD pump. This new type of EOD pump eliminates the gear train typically employed in EOD pumps, potentially reducing the size, weight, cost, complexity, and lubrication requirements of conventional EOD pumps. In an illustrative embodiment, a reciprocating electromagnetic linear actuator is employed instead of the rotating electric motor used in conventional EODs to achieve the electrical to mechanical energy conversion. An air gap between moving and stationary parts is oriented perpendicular to the direction of diaphragm motion. This orientation maximizes the amount of force that can be generated within a given volume of space.

Another illustrative embodiment of the present disclosure provides a variable stroke length EOD pump system that comprises: a diaphragm pump; an electromagnetic linear actuator that operates the diaphragm pump; wherein the linear actuator includes: two stator halves, and an armature; wherein the armature is supported for linear motion along an axis of and between field poles of the stator halves; and wherein each stator half includes a drive coil partially surrounded by a magnetically permeable core.

The above and other illustrative embodiments include a pump system that may further comprise: the armature and the two stator halves shaped and positioned such that a space between their closest surfaces forms parallel planes perpendicular to the armature's direction of motion; and an axial force acting on the armature is coupled to the pump's diaphragms through springs.

Another illustrative embodiment of the present disclosure provides a variable stroke length EOD pump system that comprises: a diaphragm pump; an electromagnetic linear actuator that operates the diaphragm pump; wherein the linear actuator includes: two stator halves, and an armature; wherein the two stator halves include drive coils and magnetic cores; wherein the armature is located in a space located between the two stator halves; wherein the armature is supported for linear motion along an axis of and between field poles of the stator halves; and a drive rod movable with the armature to move a pump diaphragm backer plate.

The above and other illustrative embodiments include a pump system that may further comprise: the armature of the electromagnetic linear actuator being movable to three different positions when the diaphragm backer plate displacement is about equal to armature displacement as the diaphragm pump is operating in low restriction, and less than the armature displacement when the diaphragm pump is operating in high restriction.

Another illustrative embodiment of the present disclosure provides a variable stroke length EOD pump system that comprises: a diaphragm pump; an electromagnetic linear actuator that operates the diaphragm pump; wherein the linear actuator includes: two stator halves and an armature; wherein the linear actuator includes two stator halves and an armature; wherein the armature is supported for linear motion along an axis of and between field poles of the stator halves; and wherein each stator half includes a drive coil partially surrounded by a magnetically permeable core, and a drive circuit; wherein the drive circuit includes a microcontroller, a position sensor for communicating the armature position to the microcontroller, an electronic switch associated with each stator coil for controlling current through the associated coil, the drive circuit including elements enabling the microcontroller to selectively operate the switches, and the microcontroller being programmed to monitor the armature's position and operate the switches at appropriate times to control the armatures motion.

The above and other illustrative embodiments include a pump system may further comprise the microcontroller being programmed to control an axial position of the armature as a function of time.

Additional features and advantages of the variable stroke length EOD pump will become apparent to those skilled in the art upon consideration of the following detailed description of the illustrated embodiment exemplifying the best mode of carrying out the variable stroke length EOD pump as presently perceived.

BRIEF DESCRIPTION OF DRAWINGS

The present disclosure will be described hereafter with reference to the attached drawings which are given as non-limiting examples only, in which:

FIG. 1 is a cross-sectional view of a variable stroke length EOD pump assembly;

FIG. 2 is a diagram view of the EOD pump of FIG. 1 at low pressure and bottom of stroke;

FIG. 3 is another diagram view of the EOD pump of FIG. 1 at low pressure and at mid-stroke;

FIG. 4 is another diagram view of the EOD pump of FIG. 1 at low pressure and top of stroke;

FIG. 5 is another diagram view of the EOD pump of FIG. 1 at high pressure and bottom of stroke;

FIG. 6 is another diagram view of the EOD pump of FIG. 1 at high pressure and at mid-stroke;

FIG. 7 is another diagram view of the EOD pump of FIG. 1 at high pressure and top of stroke;

FIG. 8 is a chart showing the EOD's force per ampere squared capability as a function of air gap.

FIG. 9 is a cross-sectional view, taken in the same plane as FIG. 1 of a computer simulation of the magnetic field induced into the magnetic circuit comprised of the stator core and armature by electrical current flowing in one of the stator coils; and

FIG. 10 is a block diagram of the complete EOD system including the electronic control.

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates embodiments of the variable stroke length EOD pump and such exemplification is not to be construed as limiting the scope of the variable stroke length EOD pump in any manner.

DETAILED DESCRIPTION

The present disclosure provides a variable stroke length EOD pump such as shown in FIG. 1. An illustrative embodiment includes a directly coupled EOD pump that employs axial air gaps 4 between its armature 6 and stators 14 so that no mechanical gear reduction is required to drive its diaphragms 10. The air gap distance is varied to assure that adequate axial force is attainable for the applied outlet restrictions. In an illustrative embodiment, a compression spring drive mechanism 12 allows relative motion between the EOD's armature 6 and pump diaphragms 10. The spring arrangement allows the magnetic air gap 4 to vary in response to the pump's outlet pressure so that high flow rates can be delivered into low restriction, and low flow rates can be delivered into high restrictions to replicate the operational performance of commercially available air operated diaphragm pumps. Movement of the EOD's armature 6 is controlled by a closed-loop PI controller monitoring the EOD's drive current and armature position.

The actuator of this EOD pump has air gaps between its moving and stationary parts oriented perpendicular to the direction of diaphragm motion. This orientation maximizes the amount of force that may be generated within a given volume of space. When its air gap is large, large electrical currents are required to produce strong actuating forces compared to when its air gap is small, and strong actuating forces can be produced with little electrical current.

As armature 6 is pulled toward energized stator core 14 it applies force to drive bushing 16 which in turn transfers the force to drive springs 12, and then to the diaphragm backer plate 18 and diaphragm 10. The pump outlet pressure produces a force to oppose the actuator force and compress drive spring 12 instead of moving diaphragm 10. When the pump outlet is unrestricted resulting in low outlet pressure, diaphragm backer plate 18 will not exert significant force on drive spring 12, and backer plate 18 will move nearly in unison with armature 6. This causes full flow rate to be achieved. In contrast, when the outlet is more restricted, the outlet pressure will exert enough force on backer plate 18 to compress spring 12 to some extent. This compression will permit armature 6 to move to a new position of smaller air gap length where sufficient force can be created within coil 8's current limitations to move fluid at higher pressure through the restricted outlet. Thus, the pump will be able to operate at higher pressure than would be possible without allowing the air gap to vary. Drive rod 20 acts as it does in a conventional AOD coupling the force applied to the driven diaphragm on the expulsion side to the opposite diaphragm to pull fluid into its fluid cap.

Again, when the air gap is large, large electrical currents are required to produce strong actuating forces compared to when the air gap is small and strong actuating forces can be produced with little electrical current. For example one embodiment of the present disclosure may employ only 0.9 units of current to produce 556 units of force across an air gap 0.010″ wide. And the same embodiment requires 20 units of current to produce 201 units of force across an air gap 0.490″ wide. That is 22 times as much current for only 36% of the force. The magnitude of currents at large air gaps is prohibitively high if high flow rates into high restriction are required. However, AOD outlet pressures versus flow rate performance curves show an inverse relationship. For example, a half inch AOD operating with a 100 psi inlet air supply may deliver about 11 gpm into 35 psi outlet pressure. But that flow may drop off to about 1 gpm at 87 psi outlet pressure. This disclosure matches characteristics of the electromagnetic actuator to the AOD performance characteristics by providing a small air gap when high outlet pressure is encountered and large air gap when low outlet pressure is present. Conventional AOD pumps may be called constant stroke length designs whereas the present EOD pump is a variable stroke length design.

As shown in FIGS. 2 through 7, armature 6 is shown in three different positions under two different operating conditions. FIG. 2 shows armature 6 at the bottom of its stroke at low pressure condition. Then, as shown in FIG. 3, armature 6 is at mid-stroke, and at a low pressure operating condition. A top of stroke condition of armature 6 is shown at FIG. 4 also at low pressure. In contrast, the view in FIG. 5 again shows armature 6 at the bottom of its stroke, but now is at high pressure. Similarly, armature 6 is at mid-stroke at high pressure in FIG. 6. And lastly, armature 6 is at the top of stroke at high pressure in FIG. 7. These figures demonstrate that the diaphragm backer plate displacement will be equal to the armature displacement when the diaphragm pump is operating in low restriction (see FIGS. 2-4), and much less than the armature displacement when operating in high restriction (see FIGS. 5-7).

Alternatively, the force of the actuator may be rigidly coupled to the pump's diaphragms, so the springs, as described above, may be removed. Using this technique, the axial distance between the stator sections would be varied either manually or automatically to achieve shorter stroke lengths for high restriction and longer stroke lengths for low restrictions.

FIG. 8 shows the coefficient in the equation relating axial force to stator current squared versus air gap distance. The magnitude of currents at large air gaps is prohibitively high if high flow rates into high restriction are required. However, AOD outlet pressure versus flow rate performance curves shows an inverse relationship. This disclosure matches characteristics of the axial flux air gap electromagnetic actuator to the AOD performance characteristics by providing a small air gap when high outlet pressure is encountered and a large air gap when low outlet pressure is present.

As a demonstrative, a magnetic flux density pattern in FIG. 9 shows flux lines from air gap 4 aligned parallel to the axis of motion 30 of the drive rod 20 and drive bushing 16. The air gap flux density will result in a magnetic pressure attracting armature 6 to stator 8. The pressure will be proportional to the magnetic flux density squared in the direction of the flux lines. The magnetic flux density is inversely proportional to the magnetic circuit reluctance which is approximately proportional to the air gap distance.

When one coil 8 is energized sufficiently, armature 6 will begin to move in the direction of its stator core 14. This motion will be monitored by a proportional and integral (PI) controller through the axial position sensor coil 22 and target 24. The PI controller will regulate the pulse width modulated (PWM) signal in response to the difference between the monitored and the desired armature motion. The PI controller of FIG. 10 provides PWM signals to the power electronics stage to deliver drive current to the EOD stator coils 8 (see, also, FIG. 1). The controller modulates and commutates the signals to achieve reciprocating motion of an armature 6 at the rate and displacement given by the user input. Only one coil 8 is energized at any time. The energized coil 8 will produce a magneto motive force (MMF) magnetizing its associated stator core 14 and the armature 6.

Although the present disclosure has been described with reference to particular means, materials and embodiments, from the foregoing description, one skilled in the art can easily ascertain the essential characteristics of the present disclosure and various changes and modifications may be made to adapt the various uses and characteristics without departing from the spirit and scope of the present invention as set forth in the following claims. 

What is claimed:
 1. An electrically operated diaphragm pump system comprising: a diaphragm pump; an electromagnetic linear actuator that operates the diaphragm pump; wherein the linear actuator includes: two stator halves, and an armature; wherein the armature is supported for linear motion along an axis of and between field poles of the stator halves; wherein each stator half includes a drive coil partially surrounded by a magnetically permeable core; a drive circuit; wherein the drive circuit includes a microcontroller, a position sensor for communicating the armature position to the microcontroller, an electronic switch associated with each stator coil for controlling current through the associated coil, the drive circuit including elements enabling the microcontroller to selectively operate the switches, the microcontroller being programmed to monitor the armature position and operated the switches at appropriate times to control the armatures motion.
 2. The pump system of claim 1, wherein the microcontroller is programmed to control an axial position of the armature as a function of time. 